This invention relates to an image forming method for use in a copying machine, a printer, a FAX machine, etc., and in particular, to a color image forming method using a flattened toner for the toner of the developer to make the image better.
Recently, with the advent of information age, the demand for office machines such as a copying machine, a printer, and a facsimile machine had been rapidly increased, and the improvement of the characteristics of said copying machine etc. to make them, for instance, have a higher speed, have a higher image quality, and bring about no environmental pollution is now required. Further, accompanied by the wide spreading of the copying machine etc. capable of making color copies, the above-mentioned improvement of characteristics to make them have a higher speed, have a higher image quality, and cause no environmental pollution has become a more important problem.
The above-mentioned problem to make the copying machines etc. have a characteristic of no environmental pollution is an important subject relating to the environmental sanitation of the operators, and in particular, in the case of copying machines etc., the high-voltage corona charging device, which generates active gases such as harmful ozone and nitrogen oxide, is a problem; for the alternative technology, a pressure transfer method aiming at a low-voltage and ozone-less process was proposed and has been put into practice. However, it has now been proved that the above-mentioned pressure transfer method is difficult to control the pressing force, and is easy to produce an uneven transfer or a poor transfer. Further, in forming a color image, it has now been proved that toner particles of a plurality of colors stacked in layers are leveled down at the time of transfer to a transfer material, to produce scattering and smudging, which makes it impossible to obtain a clear and sharp image.
On the other hand, for making a copying machine etc. have a higher image quality, it is necessary to improve the property of the toner, and in particular, it has now been proved that it is important to use a toner having a small particle diameter of 5 to 10 xcexcm and a sharp particle diameter distribution. Although such a toner can be obtained by classifying a coarsely made toner produced also by a conventional pulverization granulating method into the above-mentioned range of particle diameter, there has been a problem that the amount of toner removed by the classification process was considerably much, which made the yield lower, and productivity worse. Hence, in recent years, it has been developed a polymerization-granulated toner which is obtained by polymerization based on a suspension polymerization method, an emulsion polymerization method, or the like, and it is being put into practice. The above-mentioned polymerization-granulated toner has a comparatively small particle diameter and a harp particle diameter distribution; by using said polymerization-granulated toner, to make the image quality higher is accomplished, but here has been a problem that, because the polymerization-granulated toner was spherical, the cleaning performance was bad in the image forming process to cause toner filming to tend to occur, and the color toner particles stacked in layers at the time of color image formation became bulky, to be leveled down at the time of pressure transfer to tend to produce scattering and smudging, which made a clear and sharp color image difficult to obtain.
Further, as regards the above-mentioned subject to make a copying machine etc. have a higher speed, the improvement of fixing efficiency of a toner image on a transfer material is an important subject, and the improvement of fixing performance of the toner has been required.
Hence, for a method of improving the above-mentioned characteristics of a copying machine etc., it has been proposed a method to practice image formation using a flattened toner. For example, in the publication of the unexamined patent application H5-127420, it is proposed a technology of a flattened toner which is obtained by making spherical toner particles dispersed in a dispersion medium collide with a rotating disk at a high speed. Further, in the publication of the unexamined patent application H11-167226, it is proposed a technology of a flattened toner for use in color copying which has a diameter of 5 to 10 xcexcm, a thickness of 0.5 to 3 xcexcm, and a thickness-to-diameter ratio falling within a range of 0.1 to 0.4 and is obtained by making spherical toner particles collide with a rotating disk at a high speed. According to the above-mentioned publications, by using a flattened toner, thermal efficiency becomes larger because heat at the time of heat fixing is received by the flattened surface of the toner particles, which makes possible shortening of fixing time, and it is accomplished to make a copying machine etc. have a higher speed. Further, in the case where the above-mentioned flattened toner is used in color image formation, the color toner particles never become bulky, and a smooth image of a high quality like a silver halide photograph can be easily obtained. Moreover, to make a toner flattened is effective not only for making the toner have a small particle diameter but also for the reduction of toner consumption.
However, upon forming a color image, if yellow (Y), magenta (M), cyan (C), and black (K) toners are flattened in the same manner, a high-quality color image which is satisfactory for a user in respect to both of the picture image area and the letter image area cannot be obtained.
This invention has been proposed in view of the above-mentioned actual situation, and it is an object of the invention to provide an image forming method which does not produce poor cleaning and a hollow image defect (an image defect caused by it that toner particles are not or less deposited at the inner area of an image), not produce scattering and smudging, is capable of obtaining a clear and sharp color image which keeps a good gradation characteristic in a picture image area and has an excellent resolution and sharpness in a letter image area, causes little environmental pollution, is excellent in fixing performance, and is capable of image formation at a high speed.
As the result of diligent investigations of the inventors, this invention has been completed on the basis of the judgement that the reason for the incapability of answering the requirement of a user for image quality is that the toners of Y, M, C, and K have been flattened in the same manner regardless of the fact that the color toners of Y, M, and C have a different role from the black (K) toner in forming a color image.
Hence, the object of this invention can be accomplished by the following structure.
A color image forming method in which a color toner image is formed through superposing the layers of three color toners of yellow, megenta, and cyan and a black toner, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, and the flattening ratio d/t of the particles of said color toners is large than the flattening ratio/tK of the particles of said black toner.
Owing to the relation dK/tK less than d/t between the flattening ratio of the K toner dK/tK and the flattening ratio of the color toners d/t superposed, a high-quality color image which is excellent in gradation characteristic and granularity in color picture area and excellent in sharpness in black letter area can be obtained.
Further, the object of this invention can be also accomplished by any one of the following preferable structures (1) to (12).
(1) A color image forming method in which a color toner image is formed on an image forming member through superposing the layers of three color toners of yellow, magenta, and cyan and a black toner, and then said layers of toners composing said color toner image are transferred all at a time onto a transfer material, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) and viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, and the thickness t of the particles of said color toners is smaller than the thickness tK of the particles of said black toner.
(2) A color image forming method in which toner images respectively composed of color toners of yellow, magenta, and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto a transfer material to form a color toner image, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, and the thickness t of the particles of said color toners is smaller than the thickness tK of the particles of said black toner.
(3) A color image forming method in which toner images respectively composed of color toners of yellow, magenta, and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto an intermediate transfer member to form a color toner image, and then said toner images composing said color toner image are transferred all at a time onto a transfer material, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm), and a flattening ration d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, and the thickness t of the particles of said color toner is smaller than the thickness tK of the particles of said black toner.
(4) A color image forming method in which a color toner image is formed on an image forming member through superposing the layers of three color toners of yellow, magenta, and cyan and a black toner, and then said layers of toners composing said color toner image are transferred all at a time onto a transfer material, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ration d/t of 2 to 8 represented by the ratio of said equivalent circular diameter d to said thickness t, and the flattening ratio d/t of the particles of said color toners is larger than the flattening ration d/tK of the particles of said black toner.
(5) A color image forming method in which toner images respectively composed of color toners of yellow, magenta, and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto a transfer material to form a color toner image, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circular diameter d to said thickness t, and the flattening ration d/t of the particles of said color toners is larger than the flattening ratio d/tK of the particles of said black toner.
(6) A color image forming method in which toner images respectively composed of color toners of yellow, magenta, and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto an intermediate transfer member to form a color toner image, and then said toner images composing said color toner image are transferred all at a time onto a transfer material, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness and the flattening ratio d/t of the particles of said color toner is smaller than the flattening ratio d/tK of the particles of said black toner
In the above-mentioned structures (1) to (6), the following conditions (a) and (b) are set for the shape of the particles of color toners of Y, M, and C and black toner of K.
(a) The thickness t of the particles of the color toners is made smaller than the thickness tK of the particles of the black toner. By using flattened toners satisfying the above-mentioned condition, the thickness of the toner layers at the superposition area (an area where color toner particles are deposited) can be made thin; therefore, a high-quality image like an image to be produced by printing can be obtained. On the other hand, because the toner layer become able to secure a certain degree of thickness in a letter area, a letter image which is excellent in sharpness is formed. FIG. 2(a) is a schematic drawing showing such a state of toner deposition.
(b) The flattening ratio d/t of the particles of the color toners is made larger than the flattening ratio dK/tK of the particles of the black toner. By using flattened toners satisfying the above-mentioned condition, the toner particles are deposited as laid down in the superposition area; therefore, even a small amount of toner particles can cover the surface of a transfer material, and the color reproducibility is excellent, while toner consumption can be reduced. On the other hand, because the toner layer becomes piled up to some extent in a letter area, a letter image having an excellent sharpness can be formed. FIG. 2(b) is a schematic drawing showing such a state of toner deposition.
(7) A color image forming method in which toner image is formed on an image forming member through superposing the layers of three color toners of yellow, magenta, and cyan and a black toner, and then said layers of toners composing said color toner image are transferred all at a time onto a transfer material, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, and the equivalent circle diameter d of the particles of said color toners is larger than the equivalent circle diameter dK, of the particles of said black toner.
(8) A color image forming method in which toner images respectively composed of color toners of yellow, magenta, and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto a transfer material to form a color toner image, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, and the equivalent circle diameter d of the particles of said color toners is larger than the equivalent circle diameter dK of the particles of said black toner.
(9) A color image forming method in which toner images respectively composed of color toners of yellow, magenta, and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto an intermediate transfer member to form a color toner image, and then said toner images composing said color toner image are transferred all at a time onto a transfer material wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, and the equivalent circle diameter d of the particles of said color toners is larger than the equivalent circle diameter dK of the particles of said black toner.
(10) A color image forming method in which a color toner image is formed on an image forming member through superposing the layers of three color toners of yellow, magenta, and cyan and a black toner, and then said layers of toners composing said color toner image are transferred all at a time onto a transfer material, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, the equivalent circle diameter d of the particles of said color toners is larger than the equivalent circle diameter dK of the particles of said black toner, and the thickness t of the particles of said color toners is smaller than the thickness tK of the particles of said black toner.
(11) A color image forming method in which toner images respectively composed of color toners of yellow, magenta, and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto a transfer material to form a color toner image, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 10 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness t of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, the equivalent circle diameter d of the particles of said color toners is larger than the equivalent circle diameter dK of the particle of said black toner, and the thickness t of the particles of said color toners is smaller than the thickness tK of the particles of said black toner.
(12) A color image forming method in which toner images respectively composed of color toners of yellow, magenta and cyan and a black toner are formed on a plurality of image forming members respectively, and the toner images on said plurality of image forming members are successively transferred onto an intermediate transfer member to form a color toner image, and then said toner images composing said color toner image are transferred all at a time onto a transfer material, wherein each of said color toners is a flattened toner composed of particles having an equivalent circle diameter d of 5 to 19 (xcexcm) as viewed from the direction to make the projection area maximum, a thickness to of 1 to 4 (xcexcm), and a flattening ratio d/t of 2 to 8 represented by the ratio of said equivalent circle diameter d to said thickness t, the equivalent circle diameter d of the particles of said color toners is larger than the equivalent circle diameter dK of the particle of said black toner, and the thickness t of the particles of said color toners is smaller than the thickness tK of the particles of said black toner.
In the above-mentioned structures (7) to (12), the following conditions (c) and (d) are set for the shape of the particles of the color toners of Y, M, and C, and the black toner of K.
(c) The equivalent circular diameter d of the particles of the color toners is made larger than the equivalent circle diameter dK of the particles of the black toner. By using flattened toners satisfying the above-mentioned condition, a letter image which is of high fidelity to the latent image and is excellent in resolution and sharpness is formed in a letter area (an area where black toner particles are mainly deposited). Further, in a superposition area (an area where color toner particles are deposited), developing performance is stable even in a highlight area where the amount of toner deposition is less, and a high-quality image like an image produced by printing having a good gradation characteristic can be obtained.
(d) The equivalent circle diameter d of the particles of the color toners is made larger than the equivalent circular diameter dK of the particles of the black toner, and the thickness t of the particles of the color toners is made smaller than the thickness tK of the particles of the black toner. By using flattened toners satisfying the above-mentioned condition, the toner particles are deposited as laid down in the superposition area; therefore, even a small amount of toner particles can cover the surface of a transfer material, and the color reproducibility is excellent, while toner consumption can be reduced. On the other hand, because the toner layer becomes piled up to some extent in a letter area, a letter image having an excellent resolution and sharpness can be formed.
FIG. 7 is a schematic drawing showing the state of toner deposition for the above-mentioned conditions (c) and (d).